Pump control system

ABSTRACT

A control system and method for controlling a pump having a fluid passage therein, including a sensing means for sensing fluid flow through the fluid passage wherein the control system controls the actuation period of the pump as a function of a characteristic of the fluid flow sensed by the sensing means. The sensed characteristic is the quantum rate of fluid flow through the fluid passage.

BACKGROUND OF THE INVENTION

This invention relates to pumps for pumping fluids and in particularliquids and control systems for such pumps. The invention will bedescribed in relation to a lubrication system for an internal combustionengine, although it is to be appreciated that other applications arealso envisaged.

It is important in lubrication systems of internal combustion enginesthat oil is delivered at appropriate rates to the various movingsurfaces and components of the engine. This is especially important forcrankcase scavenged two stroke internal combustion engines. In suchengines, oil is consumed during the operation of the engine and istypically not completely recirculated as in conventional four strokeengines. Therefore, the rates of oil delivery must be carefullycontrolled to ensure minimal resultant exhaust gas emissions, preventcontamination of any catalytic device of the engine due to excess oil inthe exhaust gases and to extend the period between oil refills.

Generally, the required rate of oil delivery varies widely depending onthe engine, the load and speed operating point of the engine, theprevious operating history of the engine and various other operatingconditions. For example, for some two stroke cycle engines, the fuel/oilratios can typically vary between 400:1 in low load and idle conditions,and 80:1 in sustained high load conditions. These conditions aretypically determined by various sensors and a control system may controlthe rate of oil delivery from the pump. The control system may beexternal from or integral with the pump itself.

The rate of oil delivery from the pump can however also be affected byfactors such as the viscosity of the oil and the voltage provided by thebattery supplying power for the operation of the pump. Higher thannormal oil viscosities and below normal battery voltages can result inlower than expected oil delivery rates from the pump. Other factorswhich would typically affect the oil delivery rate include blockageswithin the oil supply and/or delivery lines, air trapped within the oilsystem, or depletion of the oil supply. Furthermore, the transientchanges to the engine operating conditions such as going from a longperiod of operation at a low load and speed to a higher load and speedoperating point may affect the oiling rate in that a delayed increase inoiling rate may be desirable to account for any oil which may haveaccumulated in the engine during the previous period of operation. Ithas not however previously been possible to conveniently control thepump such that the above noted factors can be taken into account toensure correct and consistent oil or fluid delivery rates.

It is an object of the present invention to provide a pump controlsystem which takes into account at least one of the above factors.

SUMMARY OF THE INVENTION

With this in mind, the present invention provides in one aspect acontrol system for controlling a pump having a fluid passage therein,including a sensing means for sensing fluid flow through the fluidpassage, wherein the control system controls the actuation period of thepump as a function of a characteristic of the fluid flow sensed by thesensing means.

According to another aspect of the present invention, there is provideda method for controlling a pump having a fluid passage therein and asensing means for sensing fluid flow through the fluid passage, themethod including controlling an actuation period of the pump as afunction of a characteristic of the fluid flow sensed by the sensingmeans.

The characteristic of the fluid flow sensed by the sensing means isconveniently dependent on at least one of the above noted factors, andsensing of that characteristic therefore takes such factor(s) intoaccount. The sensed characteristic may conveniently be the quantum rateof fluid flow through the fluid passage.

The pump conveniently pumps fluid during actuation of the pump with thefluid flow through the fluid passage occurring during said actuation.The actuation period of the pump conveniently increases when the quantumfluid flow rate decreases, and decreases when the quantum fluid flowrate increases. Alternatively, the actuation period may be fixed to apredetermined setting.

The sensing means may include a displacement sensor for sensing thedisplacement of a flow responsive member located within the fluidpassage. The flow responsive member is conveniently displaced inresponse to fluid flow through the fluid passage, the displacement ofthe flow responsive member being dependent on the quantum fluid flowrate and/or the quantum amount of fluid ie: the volume. The displacementof the flow responsive member conveniently increases with an increasingquantum fluid flow rate and decreases with a decreasing quantum fluidflow rate and/or quantum amount. The sensing means may however include adifferent type of sensor means such as a mass flow sensor.

The fluid passage may be an inlet passage to the pump such that thesensing means senses fluid flow into the pump. Alternatively, the fluidpassage may be an outlet passage of the pump. Where there is more thanone outlet passage, a sensing means may be provided for at least one ofthe outlet passages or for each outlet passage. Similarly, where thereis more than one inlet passage, a sensing means may be provided for atleast one of the inlet passages or for each inlet passage. In thisregard, the pump may be configured to pump a number of different fluidsand such separate inlet passages may be desired to enable the supply ofdifferent fluids to a number of individual fluid delivery lines.

A flow control valve having a valve member associated therewith may beprovided to control fluid flow through the fluid passage. The flowresponsive member may be movable together with the valve member of theflow control valve. Alternatively, the flow responsive member may beformed integral with or may provide the valve member for the flowcontrol valve. The flow control valve is conveniently an inlet reliefvalve of the pump. Alternatively, the flow control valve may be anoutlet relief valve.

The control system can provide a feedback signal when displacement ofthe flow responsive member is sensed by the displacement sensor. It ispreferred that the feedback signal is only provided when thedisplacement of the flow responsive member is above a predeterminedthreshold value. This prevents or minimises the possibility of erroneousfeedback signals due, for example, to vibrational displacement of theflow responsive member or an insufficient fluid flow rate. Hence,selection of the threshold value determines the sensitivity of thedisplacement sensor. The threshold value may be set on the basis of theportion of fluid already delivered by the pump. For example, thethreshold value may indicate that about half of the fluid deliverycapacity of the pump has been delivered.

The actuation period of the pump may preferably be controlled by theattainment of the threshold value at which point the feedback signal isprovided. The control system preferably measures a time delay betweenthe start of the actuation period and the start of the subsequentfeedback signal.

This measured time delay is termed the "sensor delay time" or "SDT". Ithas been determined experimentally that the control system of the pumpmay conveniently be configured so that the pump is actuated over atleast substantially equivalent to twice the SDT to ensure full deliveryof the fluid being pumped. However, the pump may alternatively beactuated over a period at least substantially equivalent to othermultiples of the SDT. Alternatively, the control system may determinethe actuation period of the pump as a function of the feedback signal.For example, the duration of a previous feedback signal may be used todetermine the actuation period of the pump for a subsequent fluiddelivery. Alternatively, the period between the end of the previousfeedback signal and the detection of the subsequent feedback signal maybe used to determine the pumping period of the pump.

When the fluid viscosity is high, the pump typically needs to beactuated for a longer period to ensure correct fluid delivery. However,the flow responsive member will take longer to move in excess of thethreshold value resulting in a longer SDT. The control system thereforeensures that the pump is actuated for a longer period than would havebeen the case for a lower fluid viscosity. Similarly, when the voltageof the power supply to the pump is lower than normal, a longer actuationperiod is also required for correct fluid delivery as the pump will haveless "pumping force" available. Because this also leads to slowermovement of the flow responsive member resulting in a longer SDT, alonger actuation period is ensured.

In the situation where there is a blockage of the line providing fluidto the fluid passage or depletion of the fluid supply resulting in nonet quantum fluid flow rate, the control system will not provide afeedback signal. This is similarly the case where there is a blockage ofa line delivering fluid to a desired location which may result in thehydraulic lock of the pump. The control system may therefore include atimer arrangement setting a minimum and maximum period of pumpactuation. The pump may be conveniently actuated for the maximum periodif no feedback signal is received. If no feedback signal is receivedafter this maximum period of actuation then the control system mayprovide a fault indication or initiate an engine control strategy thatreduces the possibility of engine damage as hereinafter described. Thecontrol system may also provide a fixed actuation period, for examplewhere the SDT is abnormally short.

In a preferred arrangement, the displacement sensor is a "Hall Effect"sensor, and the flow responsive member may be a ferromagnetic bodyelement supported within the fluid passage. Displacement of the bodyelement produces a change in the magnetic field adjacent the sensor. Thesensor conveniently converts magnetic flux density into an analoguevoltage to thereby provide a voltage signal termed the "Hall Voltage",which varies depending on the relative position of the body element. Theflow responsive member may be elongated and the quantum fluid flow rateand/or quantum amount through the fluid passage produces a displacementof the flow responsive member. The displacement is a result of a fluidpressure gradient across the flow responsive member. The displacement ofthe flow response member can be modified by varying the pressuregradient across the flow responsive member. To this end, the flowresponsive member may be shaped so that the clearance between the flowresponsive member and the fluid passage can be varied in the directionof movement thereof to vary the pressure gradient thereacross as theflow responsive member is displaced. This can be achieved by for exampletapering or otherwise modifying the shape of the flow responsive member.

The control system preferably includes a sensor control circuit in theform of a "sample-and-hold" or "moving average circuit" whichconveniently includes a comparator unit for comparing the Hall Voltageand a second voltage derived from the Hall Voltage.

It is however to be appreciated that the processing of the Hall Voltagecould alternatively be digital in a sampled data system with sufficientresolution. The sensor control circuit of the control system preferablyprovides a feedback signal when the voltage difference between the HallVoltage and the second voltage reaches a predetermined value. The secondvoltage may be a voltage measured across a capacitor within the sensorcontrol circuit, and the capacitor voltage may be at least substantiallyidentical to the Hall Voltage prior to pump actuation. The controlsystem preferably provides a sample/hold arrangement wherein thecapacitor voltage is used as a datum voltage during pump actuation. Ator shortly after the start of the pump actuation, the capacitor may beeffectively disconnected from the Hall Effect sensor by means of aswitching unit, so that the capacitor voltage is not effected by thechange in the Hall Voltage during pump actuation. An advantage whicharises from the use of this sample/hold arrangement is that it allowsfor the inherent compensation for variance in magnetic field strength,Hall Effect signal amplification and build-up of mechanical tolerance ofthe assembly. Hence the arrangement is self-calibrating.

In a preferred arrangement, the Hall Effect sensor may also sense themagnetic flux produced by a solenoid assembly of the pump whenactivated. The magnetic flux of the solenoid assembly sense by thesensor may be a function of the proximity of the sensor to a coil of thesolenoid assembly, the magnitude of the coil current, and/or the numberof windings of the coil. The polar direction of the solenoid coil my bearranged relative to the flow responsive member so that the magneticflux of the solenoid coil is adapted to be additive with the magneticdensity due to the displacement of the flow responsive member. Thisarrangement results in enhanced and more reliable diagnostic informationbecause the solenoid coil actuation is also sensed by the Hall Effectsensor.

The control system also conveniently controls the frequency of actuationof the pump as a function of operating parameters of the engine. Forexample, where the pump is used to pump oil for use in an internalcombustion engine, the frequency of pump actuation generally increasesas the engine load and/or speed increase and generally decreases as theengine load and/or and speed decrease. The control system can determinethe oil delivery requirement by calculating the instantaneous oilrequirements over a short period, for example every 4 milliseconds, bymeans of a "look-up map". In the case of two-stroke engines, the look-upmap may relate a fuel/oil ratio to engine load and speed. Theseinstantaneous oil requirements can be integrated over time until theintegrated calculated amount is equal to that for one pump delivery atwhich point the pump can be actuated.

The control system may include dampening or filtering means to moderatethe rate of change of the instantaneous oil requirement as indicated bythe look-up map during acceleration transients i.e. during periods ofhard accelerations. During such periods, which may typically last foronly a few seconds, the actual oil requirements of the engine may notnecessarily need to be as high as that indicated by the look-up map."Dampening" the rate of change of the instantaneous oil requirementsduring such acceleration transients and only allowing the oiling rate toincrease to its target value at a fixed rate reduces the amount of workdone on the oil in pumping it unnecessarily, and can reduce the overalloil consumption rate of the engine. This system of oil flow rate dampingmay have applicability to many types of oil pumping systems.

During periods when the changes in speed and load of the engine are lessabrupt, the instantaneous oil requirements may be determined by thelook-up map as previously described. To this end, a sophisticatedcontrol means may be provided by the control system to enable transferbetween the normal "look-up map" oil requirement determination means andthe filtered oil requirement determination means in response to thecommencement or cessation of acceleration transients. Alternatively, thedegree of "dampening" could be a function of the rate of which speed andload are changing.

The control system may also provide a fault indication or initiate astrategy to extend the driving range of a vehicle or limit the power inan internal combustion engine when there is no feedback signal within apreselected time period indicating that there is little to no fluid oroil flow through the pump. For example, the control system can simplyturn on a warning light and/or warning alarm when there is no feedbacksignal to indicate to a driver that no oil is being delivered to theengine. Alternatively, in the case of two-stroke engines, a strategy ofutilising a leaner oil/fuel ratio can be implemented to extend thedriving range of the vehicle within which the engine is fitted. Inanother alternative, a power limiting strategy can be initiated to limitthe maximum engine speed and load of the engine thereby reducing thepossibility of damage to the engine. In a further alternative, thecontrol system may be arranged to stop the engine when there is nofeedback signal. The above noted strategies may also or alternatively beimplemented when the oil level within an oil reservoir of the engine isdetected as being critically low.

Further, the control system may also provide an automatic primingfunction in the case where oil priming of the engine is required onassembly of a new engine or after a service overhaul or maintenance soas to fill or refill the empty oil lines to various parts of the engine.The priming function can be manually or automatically actuated and caninitially cycle the pump through a number of fast actuations to pump theair out from the oil lines. Any feedback signal may be ignored duringthe fast actuations. At set intervals, the pump may be cycled through asmaller number of slow pump actuations to allow the sensor to workproperly and to determine whether there is any oil flow through thepump. If oil flow is detected, then the pump may cycle through a setnumber of actuations to fill the downstream oil lines. Otherwise, if nooil flow is detected after a set maximum number of pump actuations, thecontrol system can shut off the pump and optionally turn on a warninglight to indicate that a problem has occurred during the primingfunction.

Still further, this pump priming sequence or the initial part thereof,can be implemented in the case where there is no feedback signal. Thiswould help to clear any air bubbles in the oil supply line which may bethe cause of no feedback signal. Alternatively, the control system canimplement a pump priming sequence independent of a feedback sign byproviding a preset number of pump actuations.

The pump may preferably have a plurality of fluid discharge outlets andoil lines may extend from each of the discharge outlets to points oflubrication. The pump may be adapted to provide for the same ordiffering oil delivery capacities between discharge outlets. In the casewhere the oil delivery capacities are the same for a number of dischargeoutlets, it is preferred that the oil lines extending therefrom deliverthe same amount of oil therethrough for any number of pump actuationcycles. In this way, respective lubrication points receive the sameamount of oil at the same time after any number of pump actuation cyclesand hence such respective oil lines are filled at the same rate during apriming function. Accordingly, oil lines of different lengths butdelivering the same amount of oil therethrough may differ in widthsand/or have side galleries and cavities provided therealong to maintainsubstantially similar volumes in each oil line between the pump and thepoint of lubrication.

In the case where the oil delivery capacities are different for a numberof discharge outlets and a certain oil delivery ratio existstherebetween, it is preferred that the respective volumes of the oillines extending therefrom correspond to the same ratio. Hence, eventhough the discharge outlets have different oil delivery capacities,respective lubrication points each receive an appropriate amount of oilcorresponding to the above ratio at the same time after any number ofpump actuation cycles. That is, such respective oil lines are filled atthe same rate during a priming function. Similarly, this may be achievedby the provision of different widths and/or side galleries or cavitiesin the oil lines to maintain a certain oil delivery ratio therebetween.For both of the above cases, this ensures that no lubrication point isexcessively oiled or left dry following an oil priming operation.

The pump may be supplied with fluid from a fluid reservoir and a fluidlevel switch may be provided within the fluid reservoir, the fluid levelswitch providing a signal to the control system when the fluid levelfalls below a certain level.

Heating means are conveniently provided in the fluid supply linesupplying fluid to the pump to heat the fluid and thereby control theviscosity of the fluid. The heating means may be in the form of aheating trace wire or element which may be accommodated within and mayextend at least partially along the fluid supply line to the pump. Aheating element may alternatively or in addition be provided within eachof the delivery lines from the pump. The heating element may beactivated in dependence on the time delay between the start of theactuation of the pump and the subsequent sending of the feedback signal.When the time delay is in excess of a predetermined value indicating ahigh fluid viscosity, the heating element may be activated to therebyreduce the fluid viscosity. The heating element may preferably only beactivated when the ambient air temperature is below a predeterminedvalue. This prevents the heating elements being activated as a result oflow battery voltage or a blockage in the fluid line which both result ina higher time delay.

The present invention also provides a pump managed by the abovedescribed control system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more readily understood from the followingdescription of a preferred practical arrangement of the pump controlsystem as illustrated in the accompanying drawings wherein:

FIG. 1 is a longitudinal cross-sectional view of a pump controlled bythe control system and according to the present invention;

FIG. 2 is a graphical representation showing the operationalrelationship between the control system and the pump;

FIG. 3 is a practical arrangement of a control circuit of the controlsystem according to the present invention; and

FIG. 4 is a graphical representation showing oil pumping rate as afunction of time for two alternative embodiments of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring initially to FIG. 1, the illustrated pump is disclosed in theApplicant's corresponding patent application No. PM4768 by the Applicantand details of that pump are incorporated herein by reference. This pumpmay be used in the lubrication system of a two stroke internalcombustion engine and the control system according to the presentinvention will be described in relation to this practical application.

The pump 1 includes an inlet relief valve 2 having a valve member 3associated therewith which controls the flow of fluid through a fluidpassage 7. Oil flow through the fluid passage 17 can be sensed by asensing means 9. The sensing means 19 includes a Hall Effect sensor 4mounted adjacent to the fluid passage 17. A flow responsive member inthe form of an elongate body element 5 is mounted within the fluidpassage 17 and abuts the valve member 3. A valve spring 14 urges thebody element 5 against the valve member 3. It is also envisaged that thevalve member 3 and body element 5 may be an integral component or thatthe body element 5 be configured to be the valve member for the reliefvalve 2.

The body element 5 is made of a ferromagnetic material. The Hall Effectsensor 4 senses the change in magnetic field arising due to thedisplacement of the body element 5 relative to the Hall Effect sensor 4.The sensor 4 converts the magnetic flux density into an analogue voltageknown as the "Hall Voltage". The quantum fluid flow rate and/or quantumamount through the fluid passage 17 produces a displacement of the bodyelement 5 in a direction of motion along its elongated axis. Thisdisplacement is as a result of the fluid pressure gradient across thevalve member 3 abutting the body element 5 resulting in a force beingapplied on the body element 5 by the valve member 3. When the fluid flowis interrupted, the valve spring 14 and fluid backflow forces the returnof the body element 5 and Valve member 3 to their initial position.

The flow is constrained by the clearance around the periphery of thevalve member 3 and body element 5 and the fluid passage within which theabove valve member 3 and body element 5 move. To this end, the pressuregradient across the valve member 3 and/or body element can be varied asthey move in the elongated axial direction by tapering or otherwisemodifying the shape of the valve member 3 and/or body element 5. Thisenables the displacement of the body element 5 relative to the fluidflow to be varied.

It is also envisaged that other types of sensors be used, for example,capacitance effect sensors or thermistor element sensors. Alternatively,the sensing means 19 may be provided adjacent at least one of the outletpassages or discharge check valves (not shown) of the pump 1.

Oil flowing into the relief valve 2 through its inlet 6 results indisplacement of the valve member 3. This displacement is transferred tothe abutting body element 5. The degree of displacement of the valvemember 3 depends on the quantum oil flow rate. This displacement isgreater when the quantum oil flow rate is higher and is less when thequantum oil flow rate decreases. Displacement of the body element 5relative to the Hall Effect sensor 4 results in a change in the HallVoltage providing an indication of changes in the position of the bodyelement 5 and therefore also provides an indication of the quantum oilflow rate.

The control system utilises the Hall Voltage to provide a feedbacksignal which controls the period of actuation of the pump 1. FIG. 2 is aschematic graphical representation of the relationship between the HallVoltage, the feedback signal, the oil flow through the inlet reliefvalve 2 and the actuation period of the pump 1, respectively designatedas "Hall Voltage", "Sense" and "Drive", over a particular period oftime. As the pump drive is actuated (as shown at A), the Hall Voltagebegins to increase (as shown at B) due to fluid or oil flow through therelief valve 2. When the Hall Voltage reaches a predetermined thresholdvalue (shown at C), the control system provides a feedback signal (shownat D). This feedback signal is only provided after the Hall Voltagethreshold value is reached as it prevents or minimises the possibilityof erroneous feedback signals due to other factors such as vibration ofthe pump 1 or the presence of air bubbles resulting in smalldisplacements of the body element 5. The Hall Voltage varies as afunction of the portion of the oil already delivered by the pump. Thethreshold value may therefore be set at a level related to a particularamount of oil delivery. For example, the threshold value may be set atthe point when about half of the oil delivery capacity of the pump hasbeen delivered. This value can be determined empirically.

The Hall Voltage threshold value provides a means of controlling theactuation period of the pump. The control system includes a timing meanswhich measures the time delay between the start of the actuation of thepump 1 and the start of the feedback signal which is provided when theHall Voltage reaches the threshold value. This measured time delay istermed the "sensor delay time" or "SDT". Because the threshold value isset on the basis of the portion of oil already delivered by the pump,the pump actuation period can therefore conveniently be a function ofthe SDT.

It has been determined experimentally that by actuating the pump over aperiod at least substantially equal to twice the SDT, this generallyensures full oil delivery from the pump. The control system can then beconfigured to actuate the pump over this period. It is howeverappreciated that the SDT is dependent on the setting of the Hall Voltagethreshold value. The pump can therefore alternatively be actuated over aperiod at least substantially equivalent to other multiples of the SDT.

In an alternative arrangement, the pump actuation period can be afunction of the feedback signal, with the control system determining theactuation period on the basis of the feedback signal. The actuationperiod may be determined from the duration of the preceding feedbacksignal. Alternatively, the actuation period can be determined from theduration between the end of the previous feedback signal and thedetection of the subsequent feedback signal.

This control arrangement allows the control system to take into accountfactors such as higher than normal fluid viscosity and lower than normalbattery voltage. At lower temperatures, the fluid viscosity increasesand this higher fluid viscosity generally results in a lower quantum oilflow rate through the inlet relief valve 2. It is therefore necessary toactuate the pump 1 for a longer period because of the higher pumpingloads on the pump 1.

A lower than normal battery voltage also results in a lower quantum oilflow rate through the inlet relief valve 2. Accordingly, a longeractuation period for the pump 1 is required because the pump 1 will haveless "pumping force" available. In both of the above two situations, alonger SDT will be measured by the control system due to the longerperiod required for the feedback signal to be generated resulting in therequired longer period of actuation of the pump 1. Hence, the higher oilviscosity or lower battery voltage conditions are suitably accounted forby the control system.

It is also possible for the control system to take into accountblockages in the oil supply line to or from the pump 1 or a lack of oilflow due to depletion of the oil supply. In these situations, therewould be no oil flow through the relief valve 2 resulting in no changein the Hall Voltage. The control system would not therefore provide afeedback signal indicating oil flow through the fluid passage 17. Atimer arrangement can be provided in the control system to set a minimumand maximum duration for the actuation of the pump 1, typically between60 milliseconds to 512 milliseconds. When no feedback signal isprovided, for example because the oil is too cold and has an extremelyhigh viscosity, or where the feedback signal is continuous, the pump isactuated for the maximum period. A fixed actuation period of typically200 milliseconds may also be set when the SDT is too short, eg: lessthan 12 milliseconds. This fixed actuation period is cleared onreceiving a valid feedback signal.

The Hall Effect Sensor 4 can simply be preset to provide a signal forthe control system when the Hall Voltage reaches upper or lowerthreshold limits. There are, however, certain disadvantages to thiscontrol arrangement. It cannot take into account variations in themagnetic strengths of individual systems or effects arising fromenvironmental factors such as temperature and vibration. Long termeffects such as changes in the magnetic field due to the ageing of theferromagnetic body element 5 cannot also be taken into account.

Furthermore, each system needs to be individually calibrated to properlyposition the body element 5 relative to the sensor 4 leading toadditional costs and difficulties in the production of the pump 1.

To avoid these problems, the control arrangement can be adapted tomeasure voltage differences between the Hall Voltage and a secondvoltage derived from the Hall Voltage. The Hall Effect sensor 4 inconjunction with such a control arrangement takes into accountmanufacturing tolerance variation of various features such asferromagnetic intensity, Hall Effect gain and offset, varying distancesbetween the ferromagnetic and hall Effect elements and also overcomesthe necessity of manual calibration of the control system.

Referring to FIG. 3, the control system includes a sensor controlcircuit 11 which communicates with an electronic control unit (ECU) ofthe engine. The Hall Voltage is measured at the positive terminal 7b ofa comparator unit 7 and compared against the voltage across a capacitor8, measured at the negative terminal 7a of the comparator 7. The sensorcontrol circuit 11 may be formed as part of the ECU or part of the pumpitself.

Prior to actuation of the pump 1, the voltage across the capacitor 8 isat least substantially equal to the "steady state" Hall Voltage which isthe low voltage condition prior to oil flow through the fluid passage 17and displacement of the body element 5. At or shortly after actuation ofthe pump 1, a switching unit 9, which is shown as a FET in the sensorcontrol circuit 11 effectively disconnects the capacitor 8 from the HallEffect Sensor 4, such that the capacitor voltage is held at the "steadystate" Hall Voltage. The comparator unit 7 subsequently compares theactual Hall Voltage and the capacitor voltage.

When the voltage difference between the Hall Voltage and the capacitorvoltage reaches a certain predetermined value, the control systemprovides the required feedback signal. This sensor control circuit 11provides therefore a sample/hold arrangement wherein the capacitorvoltage is used as a "floating" datum voltage which is held steady atthe start of the pump actuation. This floating datum voltage ensuresthat system variations such as those previously referred to andenvironmental factors are taken into account. Furthermore, the measuredvoltage difference is independent of the actual position of the bodyelement 5 relative to the sensor 4, thereby eliminating the need tocalibrate the sensor arrangement. For example, as the frequency of thepump actuation increases, there is less time for the valve member 3 andbody element 5 to return to and abut the valve seat 10 of the reliefvalve 2. This results in a gradual shift of the mean position of thebody element 5 away from the valve seat 10. This shift will however noteffect the operation of the above noted control arrangement.

It is also possible to eliminate the switching unit 9 of the sensorcontrol circuit 11. Because of the inherent delay in the change in thecapacitor voltage, a voltage difference can still be measured betweenthe actual Hall Voltage and the capacitor voltage. However, becausethere will still be a slow change in the capacitor voltage, thedifference will be less than provided by the above circuit leading to apotentially poorer signal/noise ratio. Nonetheless, this may be morethan satisfactory for reduced specification and/or lower cost systems.

A side benefit of having such a sensor control circuit 11 is that itprovides a means of checking for the presence of the pump 1, and/or forchecking whether the pump 1 is properly connected to the power supplyand sensor control circuit 11 prior to start up of the engine. When theECU together with the sensor control circuit 11 are first powered upimmediately prior to engine start up, there is an initial charging ofthe capacitor 8 which causes a feedback signal to be generated when theoil pump 1 is physically present and/or properly connected to the ECU.The capacitor 8 is not however charged if the oil pump 1 is not presentand/or properly connected. In this situation, no feedback signal isgenerated. The ECU preferably corresponds with a warning light or otherwarning means which could be actuated before the engine is actuallystarted up and run if no such signal is received. This provides a checkfor the proper replacement and/or connection of the oil pump 1following, for example, service maintenance.

The control system also controls the frequency of actuation of thepump 1. It is generally necessary to increase the frequency of pumpactuation as the engine load and speed increases. Typically, in the caseof a three cylinder two stroke engine with a pump 1 having a pumpingcapacity of 0.1 CC, the period between pump actuations may vary betweenup to 350 seconds when the engine is idling and only 0.7 seconds whenthe engine is at maximum load.

The above system may be further enhanced by enabling the Hall Effectsensor 4 to also sense the magnetic flux of the solenoid coil 16 duringthe operation of the solenoid assembly 15. There are therefore twomagnetic flux component to be sensed by the Hall Effect Sensor 4, beingthe magnetic flux as a result of the displacement of the body element 5,and the magnetic flux as a result of the operation of the solenoidassembly 15.

The magnetic flux of the solenoid coil 16 by the Hall Effect sensor 4 isa function of the spatial proximity of the sensor 4 to the coil 16, andthe magnitude of the coil current and the number of coil turns thereof.The polar direction of the magnetic flux from the coil 16 is arranged bypolarity selection considerations of the current flow direction relativeto the selected magnetic polarity of the body element 5 so that thecomponent of increasing flux density from the solenoid coil 16 as thecoil current is increased is additive with the increased flux densitydue to the displacement of the body element 5 in a direction urged bythe increasing quantum flow rate and/or quantum amount. When the coilcurrent is reduced, this results in a reduction in the flux density fromthe solenoid coil 16. There is also a corresponding drop in the fluxdensity due to the reduced displacement of the body element 5 because ofa corresponding drop in the flow rate.

Therefore, the above system provides a combined overall signal forprocessing by the control system based on both the fluid flow rate andthe electrical actuation of the pump. It has been found that themagnetic flux of the solenoid coil 16 and of the displacement of thebody element 5 are of the same order of magnitude. In one example thesolenoid coil flux change was about 40% of the total flux change.

The above arrangement is important in achieving high quality diagnosticsin both automotive and marine systems, particularly where the pumpactivation frequency is required to be high so as to satisfy size andcost restraints. This is because the diagnostic information is enhancedand more reliable because of the addition of the signal provided by thesolenoid coil activation. This can be advantageous when the displacementof the body element 5 is somewhat sluggish due, for example, to highfluid viscosity. The signal showing that electrical activation hasoccurred has generally been found to provide a strong probability ofreliable fluid delivery. It should however be noted that a signal fromthe electrical activation only is insufficient for the system to operateproperly, a signal also being required as a result of the displacementof the body element 5.

The actuation frequency is a function of the required oil delivery ratewhich varies in dependence on the engine load and speed. Typically, thefuel/oil ratio for the engine varies between 400:1 at idling conditionsto 80:1 at maximum load conditions. To ensure that the pump 1 deliversthe correct amount of oil over widely changing engine operatingconditions, the control system calculates the "instantaneous" oilrequirements over a short period, typically every 4 milliseconds, bymeans of a "look-up map" relating the fuel/oil ratio to engine load andspeed. These instantaneous oil requirements are integrated over timeuntil the integrated calculated amount equals the pump capacity, being0.1 CC, the amount of oil delivered during each pump actuation. At thispoint, the pump 1 is actuated.

During periods of short hard acceleration (i.e. accelerationtransients), the rapid change in the engine load and speed typicallyresults in a dramatic increase in the instantaneous oil requirement asindicated by the lookup map. However, these acceleration transients mayonly last a few seconds, and it is possible that there may not besufficient time for the lubrication system of the engine to actuallydeliver the required oiling rate to the required areas of the engineprior to the end of that acceleration transient. Accordingly, for suchshort acceleration transients, it may not actually be necessary tosupply the instantaneous oil requirement during the accelerationtransient. In fact, it is likely that, for example, that oilre-circulated from the crankcase may provide sufficient additional oilto compensate for the higher oil requirement during such accelerationtransients.

The control system therefore may provide dampening or filtering means tomoderate the rate of change of the instantaneous oil requirement asindicated by the look-up map during acceleration transients. Hence, theoiling rate may only be allowed to increase to its target value at afixed rate and still facilitate sufficient oiling of the engine andengine components. When the rate of change of the engine load and speedis less abrupt, the control system can use the look-up map as previouslydescribed to determine the instantaneous oil requirements. To this end,a sophisticated control means may be provided by the control system toenable transfer between the normal look-up map oil requirementdetermination means and the filtered oil requirement determination meansin response to the commencement or cessation of acceleration transients.Further, the control means could be adapted to detect where a vehicle isbeing driven hard and repetitive hard accelerations are occurring suchthat it could revert to determining the oil requirements of the enginesolely from the normal look-up map determination means and hence counterthe hard driving of the vehicle. It is believed that moderating the rateof change of the instantaneous oil requirements during accelerationtransients can lead to significant reductions in the overall oilconsumption rate of the engine, for example, by around 20%.

FIG. 4 shows graphically an exemplary situation in which oil flowdamping is beneficial. The required oil flow rate increases from r₁ (ieat a first constant engine condition) to r₂ (ie at a second enginecondition requiring a higher oil flow rate) over time t₁ to t₂. At t₁,engine acceleration is suddenly increased in order to raise the speed tothe desired level, giving a high transient acceleration. At t₂, thislevel is reached, and acceleration is cut. From t₁ to t₂, the look-upmap reads a higher target oil flow rate of r₃, as a result of theincreased acceleration. The undamped system (depicted in the graph bythe dotted line) shows a rapid rate of increase in oil flow to thetarget rate r₃. Once the acceleration is cut at t₂, the oil flow ratefalls back to the new target rate r₂. In the damped system (depicted inthe graph by the solid line), however, the oil flow rate rises towardsr₃ at a much slower rate during transient acceleration, and does notreach the same level as that of the undamped system. At t₂, the targetoil flow rate is reset to r₂ and the actual flow rate reaches the newtarget flow rate a short time later. The shaded area 20 represents theextra work done by the undamped system in raising the fuel rate to anunnecessarily high level. This extra work increases fuel consumption asdiscussed above.

The control system also provides a fault indication or an enginecut-out/power limiting strategy. This can be achieved by the controlsystem keeping a history of failed pump actuations (i.e. wherein nofeedback signal is received) and taking necessary action in the eventthat the number of failed actuations exceeds a certain preset limit. Forexample, the status of the last 16 pump actuations may be kept whereinany missing feedback signal is considered an error. As soon as 4 out of16 consecutive pump actuations are recorded with a missing feedbacksignal, the control system can provide a fault indication, for example,a warning light or alarm, warning the driver of an oil pump flow error.Alternatively, the control system can implement a power limitingstrategy wherein the maximum engine speed and load is limited to therebyreduce the possibility of damage to the engine. The control system mayalternatively stop the engine. Alternatively, the control system mayschedule additional actuations to compensate for the failed pumpactuations.

In an alternative engine control strategy, for certain engine operatingconditions the pump is activated at a greater than normal rate toprovide more oil to sensitive or critical components of the engine. Thisstrategy may be introduced when the engine is above a certaintemperature, for example over 120° C. the temperature measured can bethe coolant temperature. This reduces the possibility of damage toengine components such as pistons and cylinder bores at high enginetemperatures. This strategy may also be conducted in conjunction withother engine power limiting strategies, for example when the fuelling tothe engine is reduced or modified to prevent the engine from running inthe high temperature region.

A similar engine control strategy of activating the pump at a greaterthan normal rate can be conducted when the engine is running below adesirable operating temperature, for example, at cold start. Theadditional oil will prevent component failure at low enginetemperatures, for example, piston tightening in a cold bore as thetemperatures of the components increase. This strategy may also be usedin conjunction with another power limiting strategy as in the previouslydescribed strategy.

A level sensor within a reservoir supplying lubrication oil to the pump1 could also be used to provide a signal for the control system when theoil level, and therefore the amount of oil remaining in the reservoir,drops below a predetermined level. The level sensor can be a float levelswitch although other sensor options are also envisaged such as athermistor element or optical reflective device. Once a low oil signalis sent by the level switch, the control system can track the remainingoil in the reservoir by counting the number of subsequent pumpactuations. A warning light can also be provided to indicate to thedriver that the oil level is low. The light may be adapted to flash at aprogressively higher frequency as the amount of remaining oil in thereservoir continues to drop.

The control system can also provide an automatic priming function. Oilpriming of an engine is required on assembly of a new engine or after aservice overhaul or maintenance to fill or refill the empty oil lines.The priming function may be manually actuated to initially cycle thepump 1 through a number of fast actuations which help to push air fromthe oil line. If the pump 1 is actuated too slowly, air bubbles may moveback towards the pump 1. At set intervals during the initial fastactuations of the pump 1, the pump 1 is operated through a number ofactuations which enable the sensor 4 to work to enable it to detect anyoil flow. Any feedback signals are ignored during the fast actuation ofthe pump 1. Once oil flow is detected, the pump 1 is then cycled througha set number of actuations to fill the downstream oil line or lines. Ifno oil flow is detected after a set number of actuations, then thecontrol system can shut off the pump 1 and a warning light canoptionally be lit to indicate that a problem has occurred during thepriming function.

Furthermore, the priming function may be automatically initiated wherethere is no feedback signal from the control system. This may be becauseof air bubbles in the oil supply line and the priming function assiststo clear the oil supply lines of these air bubbles.

The pump 1 is provided with a plurality of oil discharge outlets. Eachoutlet can have the same or a different oil delivery capacity. Oil linesextend from each discharge outlet to respective points of lubrication.

In the case where the oil delivery capacities are the same for a numberof discharge outlets, the respective oil lines extending therefrom arearranged to deliver the same amount of oil therethrough for any numberof pump actuation cycles to ensure that each point of lubricationreceives the same amount of oil following the priming function, and toprevent any of the lubrication points receiving excessive oil orremaining dry. This is achieved by the respective oil lines havingdifferent widths and/or having side galleries and cavities providedtherealong. This provides at least substantially similar volumes in eachoil line between the pump and the point of lubrication and ensures thatthe respective oil lines are filled at the same rate during a primingfunction.

In the case where the oil delivery capacities are different for a numberof discharge outlets, the volumes of the respective oil lines extendingtherefrom are correspondingly sized to deliver a correct amount of oiltherethrough for any number of pump actuation cycles. That is,respective lubrication points each receive on appropriate amount of oilwhich corresponds to the ratio of oil delivery capacities of thedischarge outlets. Again, this is achieved by the provision of differentwidths and/or side galleries or cavities in the oil lines to maintain acertain oil delivery ratio therebetween and to ensure that respectiveoil lines are filled at the same rate during a priming function. Hence,the provision of appropriately sized oil lines having certain overallvolumes in conjunction with the differing or similar oil deliverycapacities of the pump discharge outlets facilitates proper priming asdescribed hereinbefore.

It is also possible to control the oil viscosity by means of heatingelements provided in the oil supply and/or delivery lines. The heatingmeans may for example be in the form of a heating trace wireaccommodated within and extending at least partially along an oil line.The control system can for example control the operation of the heatingelement in dependence on the measured SDT. It is also envisaged that,where there is no feedback signal, the control system actuates theheating trace line to heat the oil and thereby reduce the viscositythereof. Alternatively, or in addition, the control system can actuatethe heating trace when the battery voltage is below normal.

Following on from the first noted example, heating elements may beconfigured to be activated in response to the SDT being in excess of apredetermined value which would tend to indicate a high fluid viscosity.The heating elements may also be configured to only be activated on thebasis of the SDT when the ambient air temperature, as sensed by anappropriate sensor connected to the control system, is below apredetermined value. In this way, the heating elements are preventedfrom being activated if the battery voltage is low or if there is a trueblockage in an oil delivery line, both of these conditions typicallyresulting in a longer SDT. It is also envisaged that the activation ofthe heating elements is a function of the pump actuation period or ispulse width modulated.

Nonetheless, the control system may be arranged to activate the heatingelements under these latter conditions to reduce the viscosity of thefluid to a lower level making it easier to pump. Hence, if a blockagedoes in fact exist in a fluid delivery line, reducing the viscosity ofthe fluid may result in some of the fluid, for example a thinner oil,being able to be pumped around the blockage and still reach the desireddelivery location. This may be particularly relevant in an engineapplication where the successful delivery of even a small amount of oilmay be sufficient to maintain the engine in a limp home mode ofoperation.

We claim:
 1. A control system for controlling the oil delivery rate of apositive displacement oil pump for an internal combustion engine, thepump having an oil passage located within or in fluid communication withthe pump, including a sensing means for sensing oil flow through the oilpassage, wherein the control system controls the actuation period of thepump as a function of a characteristic of the oil flow sensed by thesensing means.
 2. A control system according to claim 1 wherein thesensed characteristic is the quantum rate of oil flow through the oilpassage.
 3. A control system according to claim 2 wherein the pump pumpsoil during activation of the pump with the oil flowing through the oilpassage during said activation.
 4. A control system according to claim 2wherein the sensing means includes a displacement sensor for sensing thedisplacement of a flow responsive member located within the oil passage,the displacement thereof being a function of the quantum oil flow rate.5. A control system according to claim 4 wherein a flow control valvecomprising a valve member controls oil flow through the oil passage, theflow responsive member being movable together with the valve member. 6.A control system according to claim 4 wherein a flow control valvecontrols oil flow through the oil passage, flow responsive member beinga valve member for the flow control valve.
 7. A control system accordingto claim 5 wherein the flow responsive member is shaped so that theclearance between the flow responsive member and the oil passage variesin the direction of movement thereof to vary the pressure gradientthereacross as the flow responsive member is displaced.
 8. A controlsystem according to claim 5 wherein the flow control valve is an inletrelief valve of the pump.
 9. A control system according to claim 4wherein the displacement sensor is a Hall Effect sensor and the flowresponsive member is made from a ferromagnetic material.
 10. A controlsystem according to claim 9 wherein the pump is actuated by a solenoidassembly, and the Hall Effect sensor also sense the magnetic fluxproduced by a solenoid coil of the solenoid assembly when energised. 11.A control system according to claim 10 wherein the magnetic flux of thesolenoid coil sensed by the Hall Effect sensor is a function of theproximity of the sensor to the coil of the solenoid coil, the magnitudeof the coil current, and/or the number of windings of the coil.
 12. Acontrol system according to claim 10 wherein the polar direction of thesolenoid coil is arranged relative to the magnetic polarity of the flowresponsive member so that the magnetic flux of the solenoid coil isadapted to be additive with the magnetic density of the flow responsivemember.
 13. A control system according to claim 4 including a sensorcontrol means having a comparator unit for comparing a Hall voltageprovided by the displacement sensor and a reference voltage provided bythe comparator unit as a function of the Hall voltage, wherein thesensor control means provides a feedback signal when the voltagedifference between the Hall voltage and the reference voltage reaches apredetermined value.
 14. A control system according to claim 13 whereinthe reference voltage is at least substantially equal to the Hallvoltage prior to actuation of the pump.
 15. A control system accordingto claim 13 including a fault indication means for providing a signalwhen no feedback signal is received.
 16. A control system according toclaim 13 including means for operating an engine with a predeterminedengine control strategy when no feedback signal is received.
 17. Acontrol system according to claim 1 including control means forcontrolling the frequency of actuations of the pump as a function ofoperating parameters of the engine, and damping means for moderating therate of change of the amount of oil provided by the pump as a result ofchanges in the engine operating parameters.
 18. A control systemaccording to claim 1 including priming means for actuating the pump overa predetermined number of relatively fast actuations to provide apriming function for the engine.
 19. A control system according to claim18 wherein the pump is connectable to a plurality of oil lines of theengine for conveying oil to points of lubrication, with each said oilline being connectable to an outlet of the pump and being at leastsubstantially identical in volume between the pump and the point oflubrication.
 20. A control system according to claim 19 wherein the oillines are of different widths and/or include side galleries and cavitiestherein.
 21. A control system according to claim 19 including heatingmeans provided in an oil supply line to the pump for controlling theviscosity of the oil being supplied to the pump.
 22. A control systemaccording to claim 1 including heating means to heat the oil within oilsupply lines providing oil to the pump to thereby control the viscosityof the oil.
 23. A control system according to claim 22 wherein theheating means are activated in dependence on a measured time delay. 24.A control system according to claim 22 wherein the heating means areactivated in dependence on the pump activation period.
 25. A method forcontrolling the oil delivery rate of a positive displacement oil pumpfor an internal combustion engine, the pump having an oil passagelocated within or in fluid communication with the pump, and a sensingmeans for sensing oil flow through the oil passage, the method includingcontrolling an actuation period of the pump as a function of acharacteristic of the oil flow sensed by the sensing means.
 26. Acontrol method according to claim 25 wherein the sensed characteristicis the quantum rate of oil flow through the fluid passage.
 27. A controlmethod according to claim 26 including increasing the pump actuationperiod when the quantum oil flow rate decreases, and decreasing the pumpactuation period when the quantum oil flow rate increases.
 28. A controlmethod according to claim 27, including sensing the displacement of aflow responsive member provided within the oil passage with adisplacement sensor, the flow responsive member being displaceable independence on the quantum oil flow rate through the oil passage.
 29. Acontrol method according to claim 28 including the displacement sensorproviding signals to a control system in dependence on the displacementof the flow responsive member, and the control system providing afeedback signal when the displacement of the flow responsive member isabove a predetermined threshold value.
 30. A control method according toclaim 29 including controlling the period of actuation of the pump as afunction of the time delay between the start of the actuation of thepump and the subsequent sending of the feedback signal.
 31. A controlmethod according to claim 30 including actuating the pump over a periodcorresponding to a multiple of the time delay.
 32. A control methodaccording to claim 30 wherein the pump is actuated over a period atleast substantially corresponding to twice the time delay.
 33. A controlmethod according to claim 30 including actuating the pump over a periodas a function of the duration of the feedback signal.
 34. A controlmethod according to claim 33 including actuating the pump over a periodcorresponding at least substantially to the duration of a previousfeedback signal.
 35. A control method according to claim 30 includingactuating the pump over a period at least substantially corresponding tothe period between the end of a previous feedback signal and thedetection of a subsequent feedback signal.
 36. A control methodaccording to claim 30 including actuating the pump over a predeterminedperiod when no feedback signal is received.
 37. The control methodaccording to claim 36 including providing a fault indication signal whenno feedback signal is received.
 38. A control method according to claim36 including initiating a predetermined engine control strategy forreducing the possibility of damage to the engine when no feedback signalis received.
 39. A control method according to claim 3 includingactuating the pump over a predetermined period when the time delay isbelow a minimum predetermined period.
 40. A control method according toclaim 25 including actuating the pump over a greater than normal ratewhen the temperature of the engine exceeds a predetermined value.
 41. Acontrol method according to claim 25 including activating the pump overa greater than normal rate when the temperature of the engine is below apredetermined value.
 42. A control method according to claim 25including cycling the pump through a number of relatively short periodsof actuation to pump oil during a priming function for the engine.